IM-P157-38
CMGT Issue 4
10
Steam/Water Mixing Stations (MkII valves - 2002 onwards) Safety and Operation
500
400
300
200
100
0
0 1 2 3 4 5 6 7 8 9 10
40 °C
50 °C
60 °C
70 °C
80 °C
90 °C
350
300
200
100
0
0 1 2 3 4 5 6
7 8
9 10
40 °C
50 °C
60 °C
70 °C
80 °C
90 °C
100
75
50
25
0
0 1 2 3 4 5 6
7 8
9 10
40 °C
50 °C
60 °C
70 °C
80 °C
90 °C
200
150
100
50
0
0 1 2 3 4 5 6 7 8 9 10
40 °C
50 °C
60 °C
70 °C
80 °C
90 °C
100
75
50
25
0
0 1 2 3 4 5 6
7 8
9 10
40 °C
50 °C
60 °C
70 °C
80 °C
90 °C
Supply pressure bar g
(Please note: Only SI metric figures have been used in this section)
The graphs indicate the maximum flow of hot water at various temperatures for a given steam supply pressure.
The bold line shows the maximum cold water flow for a given water supply pressure. When sizing the valve,
ascertain the hot water temperature and quantity required, and the water and steam pressure available. The
cold water and steam supply pressure should be nominally equal for satisfactory operation.
Plot the cold water supply pressure and read off from the bold line the maximum flow of cold water. Plot the
steam supply pressure against the running temperature required and read off the maximum flow of heated
water. For sizing purposes always select the lowest of the two values because depending on the supply
pressures, there can be an imbalance in the amount of either water or steam heat available. The effect of
selecting different supply pressures or different sizes of valve can easily be compared.
In the example shown below the lowest flowrate plotted is 32 l/min. If the required hot water flowrate was 30
l/min. then the
½
" mixing valve would be suitable. If the required hot water flowrate was 37 l/min we would
need to select a
¾
" mixing valve (although the
½
" mixing valve can pass 40 l/min of cold water), since the
lowest flowrate plotted must exceed the required hot water flowrate.
Sizing example:
For cold water supply pressure of 3 bar g
the maximum flow of cold water is 40 l/min.
For steam supply pressure of 3.5 bar g the
maximum flow of hot water at 50
°C is 32 l/min.
S
up
pl
y p
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ss
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ar g
3. How to size
